The present invention relates, in general, to the desulfurization of flue gas and, in particular, to a new and useful method for treating seawater after scrubbing the flue gas with seawater.
It is well-known that seawater can be used to scrub SO.sub.2 amounts from boiler flue gases. This is known as "seawater scrubbing". The active constituent in the seawater is bicarbonate. Seawater has a natural pH of about 8.2. During the scrubbing process the following reactions take place: EQU SO.sub.2 +HCO.sub.3.sup.- .fwdarw.HSO.sub.3.sup.- +CO.sub.2 (1) EQU 2HSO.sub.3.sup.- +O.sub.2 .fwdarw.SO.sub.4.sup.= +H.sup.+ (2)
The major constituents in fresh seawater include:
19,000 ppm chloride ion PA0 10,600 ppm sodium ion PA0 1300 ppm magnesium ion PA0 890 sulfate ion PA0 400 ppm calcium ion PA0 380 ppm potassium ion PA0 170 ppm bicarbonate ion
In addition, the seawater tends to be saturated with oxygen at about 5 ppm.
When seawater leaves the scrubber, the chemical composition has been altered by the scrubbing process. A portion of the bicarbonate is depleted by reaction (1). The sulfate concentration is slightly elevated over its background concentration, and essentially all of the dissolved oxygen is consumed by reaction (2) above. The portion of the bisulfite that is not oxidized by reaction (2) remains in the seawater as a chemical oxygen demand (COD) constituent. Finally, the pH of the seawater leaving the scrubber can be as low as 3.5. Because of these changes, the seawater cannot be returned to the ocean without first treating the water to an extent where the water will not adversely effect aquatic life.
Presently, there is no known method or system for treating effluent seawater from a seawater scrubber system which provides an efficient treatment of the seawater prior to returning to its natural source.